1. Technical Field
The present invention relates to a substrate used for an electro-optical device, for example, a liquid crystal device; an electro-optical device including such a substrate; and an electronic apparatus, for example, a liquid crystal projector, including such an electro-optical device.
2. Related Art
A liquid crystal device is an example of an electro-optical device. In a liquid crystal device, in order to prevent an image signal held in a pixel from leaking, a hold capacitor is added in parallel with a liquid crystal capacitor. Such a hold capacitor is formed in a non-opening region provided around an opening region in each of a plurality of pixels constituting a display region of the liquid crystal device. The opening region is a region surrounded by the non-opening region, and is often formed in a rectangular shape. In addition, in order to electrically connect the hold capacitor formed in the non-opening region and a transparent pixel electrode formed in the opening region above the hold capacitor, the pixel electrode is often provided with an extension located in the non-opening region over the hold capacitor, and a connector such as a contact hole is provided in the non-opening region so as to connect the extension and the hold capacitor (see JP-A-2005-301306).
The above-described known liquid crystal device has the following problems in manufacturing process and design. Liquid crystal devices are required to have a higher opening ratio to have higher image quality. However, if the widths of interconnects and the sizes of elements in the non-opening region are reduced, it is difficult to secure a space for providing a connector such as a contact hole. More specifically, for example, in the case where the width of the non-opening region is defined by the widths of interconnects, hold capacitors, and so forth provided between adjacent pixels, the opening ratio can be increased by reducing the widths of the interconnects and so forth. However, it is difficult to secure the size of a contact hole to be formed and the margin for alignment of a mask used for partly removing an insulating film when the contact hole is formed.
An advantage of some aspects of the invention is that there are provided a substrate used for an electro-optical device, such as an active-matrix addressed liquid crystal device, whose opening ratio can be increased, with the electrical connection between a hold capacitor and a pixel electrode in each pixel secured; an electro-optical device including such a substrate; and an electronic apparatus.
In a first aspect of the invention an electro-optical device substrate includes a substrate, a plurality of data lines and a plurality of scanning lines crossing each other on the substrate, and a plurality of pixels defined by the plurality of data lines and the plurality of scanning lines so as to correspond to intersections thereof. Each pixel includes a pixel electrode, a conducting layer formed in a non-opening region separating an opening region of the pixel from that of another pixel, the conducting layer having a protruding portion protruding into the opening region from a part of one of a plurality of region edges defining the opening region, and a first contact portion electrically connecting the pixel electrode and the protruding portion.
The electro-optical device substrate according to a first aspect of the invention is, for example, a TFT array substrate to be disposed opposite an opposing substrate for sandwiching liquid crystal, which is an example of an electro-optical material, or a plate-like structure including a TFT array substrate and components formed on the TFT array substrate. When an electro-optical device is in operation, each pixel is supplied with a scanning signal via a scanning line, and the pixel electrode of each pixel is supplied with an image signal via a data line. More specifically, the gate of a semiconductor element such as a thin film transistor (hereinafter referred to as “TFT”) provided in each pixel for switching the pixel is electrically connected to a scanning line and is turned on or off in accordance with a scanning signal. The pixel electrode, which is a transparent electrode formed of ITO for example, is selectively supplied with an image signal via a data line. The tilt angle of the electro-optical material (for example, liquid crystal) sandwiched between an opposing electrode provided in the opposing substrate and the pixel electrode is controlled by an electric field generated between these electrodes on a pixel by pixel basis. In accordance with the change in tilt angle, the quantity of light passing through each pixel is controlled, and an image is displayed by an active matrix addressed electro-optical device such as a liquid crystal device.
The conducting layer is formed in a non-opening region separating an opening region of the pixel from that of another pixel. The conducting layer has a protruding portion protruding into the opening region from a part of one of a plurality of region edges defining the opening region. The term “opening region” of the invention substantially means a region through which light passes, for example, a region in which a pixel electrode is formed, and a region in which the gray scale of light coming out of an electro-optical material such as liquid crystal can be changed in accordance with the change in transmittance ratio. In other words, the term “opening region” means a region in which light collected to a pixel is not blocked by light-shielders such as interconnects, light-shielding films, and various elements that do not transmit light or have a transmittance ratio lower than that of a transparent electrode.
The term “non-opening region” in the invention means a region that does not transmit light contributing to display, for example, a region in which are disposed light-shielders such as opaque interconnects, electrodes, or various elements. The higher the opening ratio, which means the ratio of the opening region to the size of a pixel including the opening region and the non-opening region, the higher the display performance of an electro-optical device including the electro-optical device substrate according to the invention.
One of a plurality of region edges defining the opening region is defined, for example, by the edge of an interconnect or an electrode formed in the non-opening region. For example, in the case where the opening region is rectangular, the term “a plurality of region edges” means four sides defining the rectangular shape, and the plurality of region edges define the shape of the opening region. Each region edge does not have to extend linearly in a particular direction but can have a portion protruding or recessed in the direction perpendicular to the direction in which the region edge extends.
In the electro-optical device substrate according to the first aspect of the invention, since the protruding portion protrudes into the opening region, the area of the opening region is small compared to the case where the protruding portion is not provided. However, in the electro-optical device substrate according to the first aspect of the invention, since the protruding portion protrudes into the opening region from a part of one region edge, the non-opening region extending along the direction in which the one region edge extends can be narrowed except for the protruding portion. More specifically, since the first contact portion is electrically connected to the protruding portion as described hereinbelow, it is not necessary to secure a space for forming the first contact portion in the non-opening region extending on either side of the part of the one region edge. Therefore, for example, by narrowing a light-shielder such as a light-shielding interconnect on either side of the part of the one region edge, the width of the non-opening region can be reduced on either side of the protruding portion, and the area of the entire opening region can be increased.
Therefore, in the electro-optical device substrate according to the first aspect of the invention, since the protruding portion protrudes into the opening region, the shape of the opening region in plan view is not strictly rectangular. However, compared to the case where the protruding portion is not provided, the opening ratio can be improved, and the image quality of the electro-optical device including the electro-optical device substrate can be improved. In addition, even in the case where the non-opening region is narrowed, a margin necessary for the etching process for forming the first contact portion can be secured.
The first contact portion is a connector such as a contact hole electrically connecting the pixel electrode and the protruding portion. In the case where the conducting layer is electrically connected to an electrode constituting an element such as a hold capacitor, the hold capacitor can temporarily hold the potential of the pixel electrode in accordance with the image signal supplied to the pixel electrode. In this case, the conducting layer functions as a relay layer for electrical connection between the hold capacitor and the pixel electrode.
In the case where the electrode of the hold capacitor and the pixel electrode are electrically connected not via the conducting layer, the electrode of the hold capacitor has a large width for forming a contact portion for connecting the hold capacitor to the pixel electrode, and consequently the non-opening region also has a large width. However, in the invention, since the protruding portion protrudes from the nonopening region into the opening region, it is not necessary to extend the entire electrode of the hold capacitor into the opening region.
As described above, in the electro-optical device substrate according to the first aspect of the invention, the opening ratio can be improved with the electrical connection between the pixel electrode and the conducting layer secured. Therefore, the image quality of an electro-optical device such as a liquid crystal device including the electro-optical device substrate according to the invention can be improved.
In the first aspect of the invention, each pixel may further include a hold capacitor and a second contact portion. The hold capacitor includes a first electrode formed in the non-opening region, a second electrode formed over the first electrode in the non-opening region, and a dielectric film sandwiched by the first electrode and the second electrode, and temporarily holds a potential of the pixel electrode in accordance with an image signal supplied to the pixel electrode. The second contact portion electrically connects the conducting layer and the second electrode in the non-opening region.
In this case, since the conducting layer is electrically connected to the first contact portion and the second contact portion, the conducting layer functions as a relay layer for electrical connection between the hold capacitor and the pixel electrode.
In this case, the degree to which the opening region is narrowed is small compared to the case where the second electrode protruding into the opening region and the second contact portion are directly connected. More specifically, it is preferable to pattern the first electrode and the second electrode so that the area of the overlap between the first electrode and the second electrode is larger, and to thereby increase the capacity of the hold capacitor so as to improve the ability to hold the potential of the pixel electrode. However, to extend the second electrode into the opening region throughout the one region edge is not a preferable design from the viewpoint of improving the opening ratio. Therefore, by electrically connecting the pixel electrode and the hold capacitor via the conducting layer, the part of the second electrode protruding into the opening region can be reduced, and the decrease in the opening ratio can be prevented.
In the first aspect of the invention, each pixel may further include a hold capacitor and a second contact portion. The hold capacitor includes a first electrode formed in the non-opening region, a second electrode formed over the first electrode in the non-opening region, and a dielectric film sandwiched by the first electrode and the second electrode, and temporarily holds a potential of the pixel electrode in accordance with an image signal supplied to the pixel electrode. The second contact portion electrically connects the pixel electrode and the second electrode in the non-opening region.
In this case, the hold capacitor and the pixel electrode can be connected not via the conducting layer functioning as a relay layer.
In the first aspect of the invention, the first electrode and the second electrode may be metal films.
In this case, the hold capacitor has a so-called MIM (Metal-Insulator-Metal) structure. The second electrode is a pixel potential side capacitor electrode electrically connected to a data line, for example. The first electrode is a fixed potential side capacitor electrode at a fixed potential. Normally, the fixed potential side capacitor electrode extends across a plurality of pixels. Therefore, the area of the first electrode is larger than that of the second electrode. In the case where the first electrode and the second electrode are metal films, compared to the case where these electrodes are formed of a semiconductor, the power consumption of the entire electro-optical device substrate can be reduced. In addition, the elements in each pixel can operate at a high speed.
In a second aspect of the invention, an electro-optical device substrate includes a substrate, a plurality of data lines and a plurality of scanning lines crossing each other on the substrate, and a plurality of pixels defined by the plurality of data lines and the plurality of scanning lines so as to correspond to intersections thereof. Each pixel includes a pixel electrode, a conducting layer, a hold capacitor, a first contact portion, and a second contact portion. The conducting layer is formed in a non-opening region separating an opening region of the pixel from that of another pixel. The conducting layer has a protruding portion protruding into the opening region from a part of one of a plurality of region edges defining the opening region. The hold capacitor includes a first electrode extending from the non-opening region into the opening region, a second electrode formed over the first electrode, and a dielectric film sandwiched by the first electrode and the second electrode. The hold capacitor temporarily holds a potential of the pixel electrode in accordance with an image signal supplied to the pixel electrode. The first contact portion electrically connects the conducting layer and the pixel electrode in the non-opening region. The second contact portion electrically connects the protruding portion and the first electrode.
As with the above-described electro-optical device substrate, the electro-optical device substrate according to the second aspect of the invention includes a conducting layer having a protruding portion protruding into the opening region from a part of one of a plurality of region edges defining the opening region, and a hold capacitor.
Since the first contact portion electrically connects the conducting layer and the pixel electrode in the non-opening region, it does not narrow the opening region.
The hold capacitor has a first electrode extending from the non-opening region into the opening region. The protruding portion and the first electrode are electrically connected by the second contact portion. The protruding portion protrudes into the opening region from a part of one of a plurality of region edges defining the opening region. The first electrode also extends into the opening region from the part of the one region edge. Therefore, it is only necessary to extend the part of the first electrode connected to the second contact portion into the opening region. Unlike in the case where the entire first electrode is extended into the opening region, the decrease in opening ratio is small. In addition, as with the electro-optical device substrate according to the first aspect of the invention, it is possible to narrow the parts of the non-opening region extending on either side of the second contact portion along the direction in which the one region edge extends, and therefore the opening ratio can be increased.
In the case of the electro-optical device substrate according to the second aspect of the invention, the opening ratio can be improved, with the electrical connection between the pixel electrode, the conducting layer, and the hold capacitor secured. Therefore, it is possible to improve the image quality of an electro-optical device such as a liquid crystal device including the electro-optical device substrate according to the second aspect of the invention.
In the second aspect of the invention, the first electrode may be a semiconductor layer having a first portion that extends into the opening region from the non-opening region and that is not located under the second electrode, and the second contact portion may be electrically connected to the first portion.
In this case, the hold capacitor has a so-called MIS (Metal-Insulator-Semiconductor) structure. For example, an image signal is supplied to the pixel electrode via the first electrode electrically connected to the drain of a TFT formed in the non-opening region.
In the first aspect of the invention, the one region edge may extend along the direction in which the scanning lines extend, and the protruding portion may protrude into the opening region from the center of the one region edge.
In this case, the deterioration in image quality caused by an asymmetrical shape in plan view of the opening region in each pixel can be prevented.
In the first aspect of the invention, the one region edge may extend along the direction in which the scanning lines extend, and the protruding portion may protrude into the opening region from a position off the center of the one region edge.
In this case, if the protruding portion cannot be protruded into the opening region from the center of the one region edge due to the layout of interconnects or elements formed in the non-opening region, the conducting layer and the pixel electrode can be electrically connected by protruding the protruding portion into the opening region from a position off the center of the one region edge.
In the first aspect of the invention, the protruding portion may protrude into the opening region from a corner of the opening region.
In this case, the protruding portion protrudes into the opening region from a place where one region edge and another region edge meet, and interconnects and various elements in the non-opening region can be disposed more flexibly.
In the first aspect of the invention, each pixel may further include a transistor whose source is electrically connected to one of the data lines and whose gate is electrically connected to one of the scanning lines, and the hold capacitor may be disposed directly above the transistor.
In this case, light incident on the transistor can be blocked by the hold capacitor. The term “directly above” means that the hold capacitor is disposed just above the transistor and there is no light-shielding film therebetween. In this case, since the hold capacitor is disposed directly above the transistor, the hold capacitor can block light incident at a large angle with respect to the normal direction to the semiconductor layer of the transistor, and can reduce the light leak current generated in the transistor.
In the first aspect of the invention, the conducting layer may be formed in the same layer as the data lines.
In this case, the data lines and the conducting layers can be formed so as to be apart from each other in the following way. First, a thin film of a conducting material is formed in the layer in which the data lines are provided, using a thin film formation technology. Next, the thin film is partly removed. In this case, since the data lines and the conducting layers can be formed in the same process, the manufacturing process can be simplified.
An electro-optical device according to a third aspect of the invention includes the electro-optical device substrate according to the first aspect of the invention.
Since the electro-optical device according to the third aspect of the invention includes the electro-optical device substrate according to the first aspect of the invention, the electro-optical device has high display performance.
An electronic apparatus according to a fourth aspect of the invention includes the electro-optical device according to the third aspect of the invention.
Since the electronic apparatus according to the fourth aspect of the invention includes the electro-optical device according to the third aspect of the invention, it is possible to realize various electronic apparatuses, such as a projection display apparatus, a cellular phone, a personal digital assistance, a word processor, a viewfinder-type or monitor-direct-view-type video tape recorder, a workstation, a video phone, a POS terminal, and a touch panel, that are capable of high-quality display. In addition, an electrophoretic apparatus such as an electronic paper can also be realized.
The above-described advantage of the invention will become apparent from the following description of exemplary embodiments.